1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) which employs a voltage control birefringence method for controlling tilt directions of liquid crystal by using an electric field, and in particular to a driving circuit of such an LCD.
2. Description of the Prior Art
LCDs, in which liquid crystal is enclosed between a pair of substrates and a voltage is applied to the enclosed liquid crystal for desired display, are advantageously small and thin, and the power consumption thereof can be easily reduced. Due to these advantages, LCDs are widely used as displays in various office automation equipment, audio visual equipment, and portable or on-board devices.
In particular, a DAP (deformation of vertically aligned phase) LCD is proposed, which includes liquid crystal with negative dielectric constant anisotropy, and controls initial alignment of the liquid crystal molecules to be vertically-aligned by using a vertical alignment layer. Specifically, a DAP LCD employs one type of electrically controlled birefringence (ECB) methods, and controls transmittance and displayed colors of the light coming into the liquid crystal layer by utilizing a difference in a reflective index between the longer and shorter axes of a liquid crystal molecules, i.e., a birefringence phenomenon. A pair of substrates are provided each with a polarization plate attached on the outer surface thereof, such that their polarization directions are orthogonal to each other. When voltage is applied to the liquid crystal layer, linearly polarized light which has been introduced into the liquid crystal layer via the polarization plate on one side of the substrate is converted into elliptically or circularly polarized light due to birefringence of the liquid crystal layer, and is partly ejected from the polarization plate on the other side. Since the extent of birefringence of the liquid crystal layer, i.e., a phase difference (a retardation amount) between ordinary and extraordinary ray components of the incoming linearly polarized light, is determined according to the voltage applied to the liquid crystal layer, i.e., the intensity of an electric field caused in the liquid crystal, the amount of ejected light from the second polarization plate can be controlled for every pixel by controlling for every pixel the voltage applied to the liquid crystal layer. This eventually makes it possible to display a desired image as a whole.
A DAP LCD is originally superior in light transmittance as it utilizes birefringence, and can be made without a rubbing step in a manufacturing process as a result of improvement of a panel structure, or the like, of the display. Moreover, the display can have an improved viewing angle. However, when voltage is applied to vertically-aligned liquid crystal, tilt directions of the respective liquid crystal molecules may vary even though the tilt angles thereof are the same. Therefore, it takes some time until the liquid crystal molecules within one pixel region come to have the same tilt directions. This may problematically slow a response time of liquid crystal molecules with respect to the applied voltage.